Thermal circuit interrupter



March 9, 1943. E. H. TAYLOR THERMAL CIRCUIT INTERRUPTER Filed June 9, 1938 Qwg 4 Patented Mar. 9, 1943 2,818,281 THERMAL CIRCUIT INTEBRUP'I'EB Elmer H. Taylor, Newbaryport, Mesa, assignor to The Chase-Shawmut Company, Newbnryport. Malia, a corporation of Massachusetts Application June 9, 1938, Serial No. 212,735

lliClaims.

'I'hisinvention relates to fusible protective devices employing a conducting structure having separable parts maintained in circuit closed connection by a readily-fusible low melting temperature material which is adapted to be melted to permit the separation of the parts and the interruption of the circuit.

In a device of this type it is common to provide an electric resistance element to heat the fusible mass and a fuse link to provide for the instant interruption of the circuit upon a severe overload approaching a short-circuit.

It is one of the objects of the present invention to simplify the construction of such a protective device and at the same time to improve the operation thereof by utilizing the heat generated in the fuse link to melt the fusible mass and eflect interruption of the circuit upon long continued small overloads, thereby eliminating the heating resistor.

It is also an object of the present invention to control the time required for the readily fusible material to melt when the device is traversed by an overload current that is not sufficient to fuse thefuselinkbytheuseofafuselinkone end of which is normally anchored by the fusible material, the link having such mass, preferably concentrated near the fusible material, that the elevation in temperature of that end of the link that is anchored by the fusible material to the melting point of the material is delayed for the desired period of time.

Another object of the invention is the provision of a device of the general type above set forth wherein the dissipation of heat by conduction from the fusible material externally of the device is controlled.

A yet further object is generally to improve the construction and operation of fusible protective devices.

The device of the present invention in one of its aspects comprises an enclosing body of the plug fuse type having a terminal and a center contact wherein the fusible material is located in the center contact and the fuse link is connected releasably to the center contact by the fusible material and is also connected to the terminal. In this respect this application ts a continuation in part of the copending application of Morris E. Wood, assigned to the assignee of this appli cation. Serial No. 32,385, flied July 20, 1935, on which Letters Patent No. 2,168,815 were granted August 8, 1939. 7

Fig. 1 is a plan view of a fusible protective device of the plug fuse type embodying the present invention.

Fig. 2 is a sectional elevation taken along line HofFlg. lwiththe partsincircuitclosed position, the device being illustrated as positioned within a receptacle.

Fig. 3 is a section similar to Fig. 2 of the device per se but with the parts in circuit open position in response to the fusing of the fusible mass.

Fig. 4 is a plan view of the structure of Fig. 3 illustrating the position of the movable parts in circuit open condition.

Fig. 5 is a sectional elevation of the device similar to Fig. 2 but with the parts in open circuit position resulting from the fusing of the fusible link.

Fig. 6 is a view similar to Fig. 2 but illustrating a modified form of device of the so-called nontamperable type and having a modified arrangement of its current responsive parts.

Fig.7isaplan viewofthefuselinkofFig. 2. Fig. 8 is a longitudinal section of a modified form of the device in a cartridge type of enclosing casing.

Fig. 9 is a view similar to 11g. 8 but showing a further modified form of device. Figs. 1 through 6 illustrate the invention as applied to a device of the plug fuse type. The device includes a cylindrical insulating enclosing casing I! of porcelain, for instance, having the bottom wall II at one end, the radially outstanding flange II at the other end, and a chamber it open at the flange end of the body and closed by the integral bottom wall II. The open end of the chamber is closed by a transparent closure disc 20, as mica, for instance, held in place by an overlying metal cap 22 having a window .20 therein which confronts the chamber ii. The cap has a rim 26 which encircles the flange ii and the lower edge part 28 of the rim is inturned under the flange. The body I! is provided with a terminal in the form of an externally screwthreaded metal shell SI which is located on the cylindrical portion of thebody. A center contact 82, formed as a tubular rivet, extends through the middle portion of the end wall it and is fixed in place. The center contact has a recess or well 30 in its inner end accessible to the chamber II. A body or mass 16 of readily fusible metal is located within the recess 34. The solid body 35 of the contact between the bottom of the well and the contact face is sumciently long to prevent harmful dissipation of heat by conduction from the fusible mass to the terminal of the receptacle.

A fusible link 38 is located within the chamber i8 and has one end thereof connected to the center contact by being imbedded in or attached to the normally solid readily fusible metal 38. The link extends upwardly within the chamber and thence approximately horizontally to the top of apassage llinthesidewallofthebody lzand thence downwardly to the bottom of the passage where it is connected throu h a mass of solder 42, or otherwise, with the screw shell ill.

Spring means are associated with the link to withdraw it from the readily fusible mass when saidmassmeltsandreleesesiisboidonthelink. saidspringmeansineludesaspringwirellhaving one end 48 depending downwardly andseatedremovablyinaverticalrecessinashoulderll oftheplugbody. Thespringhasaportion Ill extendedatrightanglestotheendpartlland generallyparalleiwiththe horiaontalpartofthelinkandatonesidethereof whichinthemiddlepartofthecasingha a downwardly depending part I: that has a horinontal lower part II that is located under the linkandexertsanupwardtensionthereon. The linkpreferablyisprovided witha transverseloop it in which the spring end 54 is located. The portton SI of the springwire isswung from the substantially horizontal position shown inFig. 3 to the position showninl-ig.2which places the spring wire under tension when the fuse is being assembled. The portion 54 of the spring wire actsas a hook and preventsany appreciable rotationofthewireabouttheporflon. Between thespring andthecenter contact and preferably nearbutunderthespringthelinkhasareduced cross-sectional area provided conveniently by the perforation I8 whichislocatedinthemlddle part ofthelink and determinesthefusingpolnt of the link upon short-circuit. Thecross sectional area of the link at the perforation determines the overload blowing current and alsois asource ofheatseneration.

Thenatureofthematerialofthelinkandthe dimensions thereof depend upon the characteristicsofthecircuittobeprotected. Thelink may comprise a flexible copper strip or ribbon which has been found to be highly satisfactory.

For some purposes, however, the link can be composed of a flexible strip of material having greater electrical resistance than copper and thereby greater heat generating property such, for instance, as a strip of copper-nickel alloy of suitable dimensions. The strip ll of whatever material it is composed constimtes both the fusible link which protects the circuit against short-circuit currents and the heater for the fusible mass ll. The readily fusible metal I! is an alloy, or a single metal, having a melting temperature preferably lower than the melting temperature of the link.

A fuse link generates heat when traversed by an electric current and the heating ofthelinkishereinutilisedtomeltthefusible mass It. It is apparent that heatwill be transmitted iromthelinktothefusihlemass and whenthetemperatureofthe fusiblemassbecomes sui'ilciently high it will melt and release its grip ontheendofthelinhtherebypermitting thespringtopullthelinkoutofthefusiblemass into some position as illustrated in Fig. 3, and thereby interrupt the circuit. In the circuit open position the link is in substantial contact with that disc 20 oratleast the released partsareclosertheretothanbeforeoperationso thattheopencircuitconditionofthedevioecan bedisoernedreadily. Themetalmasstlisintendedtofuseabmtthelinkandinterruptthe circuitwhentbedeviceistraversedforasubstantial period of time by an overload current which,however,isnotgreat enoughto cause the thespringiseifective in widening theclrcuitintermptingnpasillustratedinl 'igj.

The desired delay in heating the fusible mass tothemelting temperaturcwhenthedevice'is traversed by moderate overload is herein obtained by a heat absorbing member Ill attached to the fuse link preferably between the short-circuit perforation It and the fusible mass it. The heat absorbing member as here shown comprises a cylindrical button having a projection 62 on one end face which is extended through a perforation of the link and is headed over thereupon so that the end face of the button is in good thermal contact with the link. The button preferably is of a material as copper that has high thermal conductivity and specific heat and the amount of material of the button is selected to obtain the desired time lag of melting of the fusible mass ll. It is apparent that the temperature of that end of the link imbedded in the fusible mass ll cannotriseintemperatureanyfasterthanis' permitted by the absorption of heat by the button and hence the heat absorbing property of the button largely control the time delay of melting of the mass 38. Preferably the button 60 is relatively close to the fusible mass so that the length of link intervening between the metal mass and the button does not generate much heat.

Thefuselinkattheendpartpassingwithin the channel II and soldered to the screw shell II is preferably enlarged as at 64, Fig. 7, so that the heating portion of the link is the narrow part ofthelinkandthereduced areapartatthe perforation 58 and variable amounts of solder ll do not seriously influence the operating characteristics of the device.

In the modification illustrated in Fig. 6 the device is of the non-tamperable type. In this modification the insulating plug body Ila has a hexagonal recess It in the end face of the end wall a thereof in which the hexagonal end wall I of a cylindrical tubular tamper preventing member II is received so that relative motion between the tamper preventing member and the plug body isprevented. 'I'hebottom end ofthe tamper preventing member is provided with teeth 12 and interpomd indentations. The tamper preventingmemberisadaptedtooooperate withacomplementary member, not here shown, located in the fuse receptacle for dislodging any foreign terminal bridging conducting matter that may be inserted therein. The center contact of this modiiication of device comprises a long tubular member'llthe lowerend Ii ofwhichislocatedbelow the tamper-preventing member I! and is adapted to make contact with the center contact of the receptacle receiving th device. The tubular contact is provided with outstanding flanges II and It which secure the contact member to the plug body and anchor the tamper preventing member I! thereto. The wall of the contact member is intendedtobesumcientlythinifmadeofgood heat conducting material, or is suiliciently long toprovideasuitablethermaldropbetween the tmandbottomendsthereof. Amassofreadily fusible material llding to the fusible masstlislooatedintheupper endofthetubular contact. Inthismodiilmtionthefuselinklla having the most readily fusible portion "a and nbythespringflhasitscndamal rlvetedtoonemdoftheheatabsorbingbutton lla. Theotherendofsaidbuttoniselectrlcally connectedtotheoentercontactmemberbrthe fmibkmssll whichcanbeindirectoontact will fuse instantly at the perforation and It withthelwercndfaceorwithasmailerpmlecbutton whereupon thespring ll moves the button and the fuse link away from the mass. thereby opening the circuit. The rate of temperature rise m reduced by the heat absorbing capacity of the button.

Figs. 8 and 9 are longitudinal cross sections of a cartridge type of device employing the present invention. Fig. 8 representing a construction adapted for currents say up to 15 amperes, and Fig. 9 representing a construction adapted for higher currents. The devices of both of these figures include a tubular insulating casing If having end caps 84 and it thereon. A fusible link II is extended through the casing and connected to the end wall of the end cap Ill by a suitable means. as solder llli, having a melting point suillciently high so that the solder is not adapted to melt during operation of the device. The other end of the link is connected to the end wall of the other end cap 84 by a mass 82 corresponding to the mass it of Figs. 2, 3 and 5, of readily fusible or low melting temperature solder. The link is provided with a perforation It or other equivalent means for forming a reduced cross section of the link to provide a more readily fusible portion on short-circuit current. The reduced cross sectional area of the link at the perforation is also a source of heat as is the case with the perforation so of the previous modifications. The heat absorbingblock It of copper or other good heat absorbing material is secured to that portion Isa of the link between the perforation Us and the fusible mass 82 and in good heat conductivity with the link to secure the desired delay of fusing of the fusible solder 82. or that portion thereof in direct contact with the link. A tension spring I8 has one end connected to the link as by being connected to the heat absorbing block 90 to pull the end of the link from the fusible mass when the latter releases its hold on the link. The. other end of the spring is provided with a hook illl which islhooked over the end of the enclosing casing under the end cap as or is otherwise anchored.

Essentially the same arrangement is embodied in the construction illustrated in Fig. 9. In this modification the enclosing casing is provided with two compartments formed by an internal ledge I02 01' the enclosing casing and an insulating disc or washer I08 which is seated upon the ledge. The tension spring in this instance is anchored to the disc and holds it seated upon the ledge. The fuse link extends through the disc and in the left end chamber III! is provided with a locality of reduced cross-sectional area as by the perforation In! where the fuse is adapted to blow upon short-circuit. The chamber Hi8 can contain an arc suppressing medium H0. The perforation m can be larger than the perforation if so that the fuse link will be ruptured on shortcircuit current at the perforation I08 and within the chamber I08.

I claim:

1. A thermal circuit interrupter including terminals, a fusible link having a most readily fusible portion extended between and electrically connecting said terminals, a readily fusible metal connecting said fuse link electrically to one of said terminals, said most readily fusible portion of said link being adapted to become heated by the current traversing it and to heat and soften 7 said fusible metal, means responsive to the softening of said fusible metal to eflect separation of said fuse link and said one terminal, and means to delay the fusing of said fusible metal including a heat absorbent mass supported by and in thermal relation with said fuse link between said most readily fusible portion and said fusible metal.

2. A thermal circuit interrupter including external terminals, a conductor extended between and electrically connecting said terminals, a mass of heat absorbent material thermally connected to said conductor, a mass of readily fusible material electrically and mechanically connecting said conductor and said mass of heat absorbent material to one terminal, said conductor being adapted to become heated by the current traversing it and to heat said fusible material and to cause said material to loosen its hold on the conductor.

.and spring means acting on said conductor and and electrically connecting said terminals, a mass of heat absorbent material thermally connected to said conductor, a mass of readily fusible metal electrically and mechanically connecting said conductor and heat absorbent mass to one terminal, said conductor being adapted to become heatedby the current traversing it and to heat said fusible metal and to cause said metal to loosen its hold on the conductor, and spring means operative to effect separation of the conductor and heat absorbent mass from the heated fusible metal, said conductor comprising a fusible link supporting said mass of heat absorbent material having a part adapted to fuse to interrupt the circuit in a shorter period of time than is required for the fusible metal to release its hold on the conductor when the conductor is traversed by a sufficiently heavy current.

4. A thermal circuit interrupting device of the plug type comprising a casing having means providing screw threads and a terminal and a center contact. a conductor extended between and electrically connecting said terminal and center contact and being connected with a stationary part of said center contact by a readily fusible mass that is in thermal association with the conductor, said conductor adapted to be heated by sufllcient current traversing it for a suflicient period of,

time to effect the heating of said fusible metal to cause it to release its hold'upon said conductor, a heat absorbent mass thermally connected to said conductor, and spring means operative upon sumcient weakening of the hold between said fusible metal and conductor to effect separation of the conductor and the heat absorbent mass from the center contact.

5. A thermal circuit interrupting device comprising a casing having a terminal and a center contact, a conductor extended between and electrically connecting said terminal and center contact and being connected with said center contact by a readily fusible mass that is in thermal association with the conductor and is attached to a stationary part of said center contact, said conductor adapted to be heated by sufllcient current traversing it for a sufllcient period of time to effect the heating of said fusible mass to cause it to release its hold upon said conductor. a heat absorbent mass thermally connected to said consaid heat absorbing mass being attached to said fusible link between said portion adapted to fuse and said fusible mass.

6. The combination of a receptacle having circuit terminals at least one of which is heat dissifusible metal adherent to and mechanically connecting said conductor and that interrupter terminal that is in engagement with the beat dissipating receptacle terminal. said conductor becoming heated by the current traversing it and transmitting heat to said fusible metal, said fialble metal fusing and releasing its attachment with said conductor when said conductor is traversed by a sumciently heavy current for a sumoiently long time, and spring means responsive tothefusingofsaidfusiblemetaltoefiectseparation of the conductor and heat absorbent mass from the associated interrupter terminal.

'i. In a thermal circuit interrupter, a casing having terminals, a heating conductor extended between said terminals and having a fusing portion, a readily fusible metal attached to said conductor and one terminal and connecting them. said heating conductor having a large mass of heat absorbing material carried thereby and attached thereto adjacent said readily fusible metal to delay the fusing thereof, and means for interrupting the circuit through the interrupter in responsetothefusingofsaidreadilyfusible metal.

8. In a thermal circuit interrupter, a havingterminals,afusiblelinkhavingamost readily fusible portion extended between said terminals. a readily fusible metal attached to said fusible link and one terminal and connecting them, said fusiblelink having a large mass of heat absorbing material thereon between said most readily fusible portion and said readily fusiblemetaltodelaythefuslngofsaidfusiblemetal, and means responsive to the fusing ofsaid fusible metal to eflect separation of said fusible metal and said fusible link.

9. In a thermal circuit interrupter, a casing havingterminals. a fusible link extended between said terminals having an intermediate heating and most readily fusible sone. a readily fusible mass connectlngsaid link and a terminal and adapted to be fused by the suiilcient heating of saidlink.aheat absorbingmassconnectedwith and supported by said link between said heating and most readily fusible none and said readily fusible metal to delay the fusing thereof, and means for interrupting the circuit through said fusiblelinkinrusponsetothefusingofsaidreadily fusible metal.

10. In a thermal circuit interrupter, a casing having terminals. a fuse link extended between said terminals, amass of readily fusible metal connecting said fuse linkwith one terminal. said fuselinkhavingasaunitarypartthereofashortcircuit blowing section and a relatively large mass of heat absorbing material additional to the link between said short-circuit blowing section and said readily fusible metal to delay the fusing of the latter, and means for interrupting the circuit through the interrupter in response tothefusingofsaidreadilyfusiblemetal.

ii. In a thermal circuit interrupter, a casing having terminals, a fuse link extended between said terminals, a readily fusible metal connecting saidfuselinkwithoneterminaLsaidfuselink having an intermediate portion of reduced cross sectional area, a heat absorbing mass secured to said link between said readily fusible metal and said reduced area portion, and spring means for eifecting separation of said link from said readily fusible metal upon the fusing of the latter.

12. In a circuit interrupter, a casing having a terminalandacentercontact.afuseiinkextended between said terminal and center contact.areadilyfusiblemetalattachedtosaidfuse link and center contact. said fuse link having an intermediate portion of reduced cross-sectional area, a heat absorbent mass fixed to said link between said portion of reduced area and said readily fusible metal, and spring means acting on said link to move it away from said readily fusible metal when the latter fuses.

13. In a thermal circuit interrupter, a casing having terminals, a fuse link extended between a said terminals having a heat absorbent mass attached to one end thereof and having an interate fusing portion, a readily fusible metal connecting said heat absorbing mass with one terminal, and spring means for separating said heat absorbing mass from said one terminal and readily fusible metal upon the fusing of the latter.

14. In a thermal circuit interrupter, a casing "having terminals, a fuse link extended between said terminals having a heat absorbent mass attached to one end thereof and having an intermediatefusingportiomarcadiiyfusiblemetal the fusing of the latter, said one terminal being long and having a contact face at one end thereof and having the readily fusible metal attached to the other face thereof.

15. In a fusible electric circuit interrupter. a casing. having terminals, a fusible conductor extended between said terminals. a mass of heat absorbent material directly thermally connected to said conductor. a mass of readily fusible material electrically and mechanically connecting said mass of heat absorbent material and said conductor to one of said terminals, and spring means arranged to engage said conductor to move the conductor and the mass of heat abmrbent material away from its associated terminal for interrupting the circuit through the interrupter in response tothefusingoithereadiiyfusible metal and for separating the fused end portions of the conductor upon fusing of the fusible conductor.

a. TAYLOR.

DISCLAIMER 2,3 1 3,281.-Elmer Ta ylor, Newburyporb, Mass. THERMAL Cmcm'rIn-rmmur- TER. Patent dated March 9, 1943., Disclaimer filed November 15, 1944, by the assignee, The OTwse-Shawmut Company.

Hereby enters this disclaimer to claims 10, 11, 13, and 14 of said specification.

[Qfiic'ial Gazette December 12, 1944.] 

